Method for continuously blowing materials into molten slags

ABSTRACT

A metallurgical method and apparatus; air is continuously blown into a mixture of agglomerates of lead concentrates and carbonaceous fuel in a shaft furnace. The resulting slag is delivered from the shaft furnace into a settling tank to which the slag continuously flows while the slag is continuously delivered from the settling tank into a fuming furnace, so that the slag flows in cascade from the shaft furnace to the settling tank and from the settling tank to the fuming furnace, thereby providing a continuous flow of the treated slag from the shaft furnace through the settling tank into the fuming furnace; the slag, in addition, is continuously withdrawn from the shaft furnace.

This is a continuation of application Ser. No. 72,484, filed Sept. 15,1970 and now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 620,018 filed Mar. 2, 1967 and now abandoned.

In the treatment of slags which are in a molten condition and obtainedin the precessing of non-ferrous ores, it is necessary to blow air andcarbonaceous fuel into the molten slag. The present invention deals witha novel method of and an apparatus for providing the continuous blowingof air and carbonaceous fuel into such molten slags.

At the present time in the processing of slags which contain lead, zinc,and other non-ferrous metals, the methods are carried out in abatch-type of process so that continuous operations cannot be achieved.These known batch-methods suffer from several drawbacks, among the mostimportant of which are poor utilization of the furnace inasmuch as aconsiderable amount of time is spent simply in charging the furnace andtapping off materials therefrom; unavoidable and, in fact, inadmissiblelosses of material, as well as high labor costs; and unavoidablefluctuations in the operating temperature of an exhaust heat boilerwhich is provided to make use of the heat derived from the treatment ofthe slag and which otherwise would be wasted.

While there are indeed some known apparatuses for continuously fumingmolten slags which contain non-ferrous metals and which make use ofspecial fuming furnaces for this purpose, the known methods andapparatus have not been used in a practical way because of unavoidabletechnological difficulties and troubles which are inherent in the knownmethods and apparatus.

It is one of the primary objects of the present invention to provide amethod of and an apparatus capable of continuously processing, byfuming, molten slags which use the same type of aggregates as thosewhich are used in conventional batch processes, while providing atechnically improved method and apparatus as compared to the knownmethod and apparatus. One of the primary features of the inventionresides in arranging the molten aggregates in cascade so that there is acontinuous flow of the slag during the treatment thereof thus assuring apositive and stable control of the continuous process of the presentinvention.

With the method and apparatus of the present invention it is possible toachieve an uninterrupted tapping off of the slag from the shaft furnaceinto a settling pool where the temperature of the slag is raised byabout 100° C and where any non-ferrous metal (e.g. lead) drops which arecarried away with the flowing slag into the settling tank are separatedfrom the latter. In addition, the apparatus of the invention makes itpossible to continuously convey the slag, after treatment thereof in thesettling tank, into a slag fuming furnace from which the slag iscontinuously tapped off.

In the drawings accompanying the specification and forming a partthereof:

FIG. 1 schematically illustrates in a top plan view one possibleapparatus of the present invention for practicing the method of thepresent invention;

FIG. 2 is a view in longitudinal vertical section through the apparatus;and

FIG. 3 is a graph illustrating the height relationships of the variousparts of the apparatus of FIGS. 1 and 2.

Referring now to the drawings, there is indicated in FIG. 1, in a topplan view, a shaft furnace 1 into which a mixture of agglomerates oflead concentrates and coke is subjected to blasts of air from tuyeres ofwhich one is shown at 22. The molten non-ferrous metal, here describedas lead, is tapped off by way of a lead discharge conduit means 3 whichcommunicates with the interior of the shaft furnace 1 through a tappinghole 16 at the level of the bath of molten lead therein so that thisbath will flow out through the discharge syphon 3 to be received in asuitable ladle 21, as schematically indicated in the drawing.

A feeding syphon or conduit means 2 is provided for continuously feedingslag from the shaft furnace 1 through a port 14 into a generally coveredsettling tank 4; this feeding syphon means 2 is in the form of a tube orsyphon composed in its entirety of slag-resistant refractory materialswhich do not have any cooling elements incorporated in them, so that theslag flows continuously without cooling through the feeding syphon means2 from the shaft furnace 1 into the settling tank 4 through an opening18 in the cover of tank 4. The surface of the slag in the settling tank4 is at an elevation which depends upon the elevation of the outlet 5 inthe discharge side wall of the settling tank 4. The ends of the conduitmeans 2 are continuously open so that there is a continuous flow incascade fashion of slag from the shaft furnace 1 into the settling tank4. Furnace 1 which is substantially closed, has a stack 1a. The positivepressure in furnace 1 forces the slag and metal through the syphons.Consequently, the flow rates of the slag and metal are constant andindependent of the charge in the furnace 1.

The slag discharge port 14 is situated at the level of the bath ofmolten slag. The slag is pressed through and does not flow downwardlytoward the settling tank, but first upwardly, then downwardly andfinally in cascade fashion from the shaft furnace toward the settlingtank. In such a manner the top of the slag surface in the settling tankcan be on an elevation lower, on the same elevation, or on an elevationhigher than the slag discharge port in the wall of the shaft furnace.The same is true of the lead discharge. Consequently, it is notnecessary to arrange the shaft furnace higher than the settling tank.

The cross-sectional areas of the lead discharging port 16 and of theslag discharge port 14 are not only critical for the process, but theymust remain constant during the design life of the shaft furnace inorder to insure constant flow rates.

The molten metal is delivered by way of the lead discharge syphon 3,which entrance communicates with the interior of the shaft furnace atthe level of the bath of molten metal therein. The cross-sectional areaof the channel through the syphon has the same measurement as thecross-sectional area of the lead discharging port. The channel is in theform of a reversed V (FIG. 2). The lead flows with a constant flow rateas described hereinabove. The syphon is composed in its entirety ofslag-resistant refractory materials which do not have any coolingelement incorporated into them.

The slag flowing out from the discharge end of the syphon runs incascade fashion into the settling tank and is discharged therefrom in ahorizontal flow. Such a change in the flow directions provides for aneven distribution, good settling conditions and an even heating of theslag into the settling tank. The cross-sectional area of the outlet port5 is at least equal or greater than that of the channel through thesyphon 2. A tapping hole 17 is provided on the bottom end of the sidewall of the settling tank for periodically (every 4-5 days) tapping-offthe accumulated lead.

In the settling tank 4 the temperature of the slag is raised byelectrodes 20 (three shown) passing downwardly through the cover of thesettling tank into the slag. Electric current passing through the slagbetween electrodes heats the slag.

The apparatus of the invention locates the lead discharge syphon means 3nearer to the slag discharge syphon means 2, or feeding conduit meansfor feeding the slag from the shaft furnace 1 to the settling tank 4,than is conventional. Thus, in accordance with one of the features ofthe invention, the distance L between the axis of conduit means 2 andthe entrance of conduit means 3 is from 500 to 1500 mm, as measured in ahorizontal plane (FIG. 1), depending upon the size of the furnace 1. Thelocation of the pair of syphon means 2 and 3 closer to each otherprovides a stabilization in the operating conditions of the shaftfurnace and results in a stabilization of the uninterrupted tapping-offof the slag from the shaft furnace into the settling tank.

As was pointed out above, the slag is continuously delivered into thesettling tank 4 from the shaft furnace 1 and in the settling tank 4residual lead droplets are separated from the slag and the temperaturethereof is increased by about 100° C. In order to provide a continuousdischarge of the treated slag from the settling tank 4, a connectingslag conduit means 15 communicates with a port 5 of the settling tank,this outflow port 5 being situated at the elevation of the surface ofthe slag in the tank 4.

The connecting conduit means 15 not only communicates permanently withthe settling tank 4 but also communicates permanently with the fumingfurnace 6 which has an inlet port 7 communicating permanently with theend of the conduit means 15 distant from the port 5. The fuming furnace6 is of a rectangular configuration and has a width to length ratio ofbetween 1 :: 1 and 1 :: 6. A discharge conduit means 8 communicates withthe blast furnace 6 for continuously discharging the slag therefrom, andin accordance with a further feature of the invention the inlet port 7and the port of the fuming furnace 6 with which the discharge conduitmeans 8 communicates are situated at diagonally opposed corner portionsof the fuming furnace 6 with the port 7 situated at an elevation H (FIG.2) of at least 500 mm above the elevation of the discharge port withwhich the discharge conduit means 8 communicates, the surface of theslag in the fuming furnace 6 being situated at the elevation of thedischarge port which communicates with the discharge conduit means 8.Thus, the blasted or fumed slag flows continuously out of the fumingfurnace 6 through the discharge conduit means 8, and the slag isreceived in a chute 9 in which granulation of the slag takes place.

The fuming furnace 6 is additionally provided with an outlet port 10 anda chute 11 which are used for emptying the fuming furnace, and this port10 is closed during the normal operations. The elevation of the port 10is, of course, substantially lower than that of the discharge port whichcommunicates with the discharge conduit means 8. A mixture of air andliquid fuel is introduced into the lower part of furnace 6 beneath thelevel of the bath therein through tuyeres 19.

In order initially to charge the fuming furnace 6, a conduit 12communicates at one end with the settling tank 4 and at its opposite endwith the fuming furnace 6 through port 13 in the wall thereof; the portswhich communicate with the conduit 12 are closed after the fumingfurnace has been charged.

The 500 mm (approximately 20 inches) difference in elevation between theslag inlet port 7 and the slag outlet port 8 in the fuming furnace 6 iscritical since during the fuming process the top surface of the slagtherein is vigorously agitated (the air + fuel mixture is blown atsuperatmospheric pressure in the slag at the bottom of the fumingfurnace). In the case that the inlet port 7 is not at least at 500 mmover the outlet port 8, the slag flowing through conduit means 15 can beimpeded from entering into the fuming furnace by the slag therein beingvigorously agitated. Furthermore, the port 7 can be clogged by the slagbursts into the fuming furnace.

The rectangular cross-section of the fuming furnace 6 is imposed by thecontinuedness of the process. Any direct flow of slag from the inlet ofthe furnace towards the outlet thereof must be avoided. The slag bathinto the furnace must be as uniform in concentration as possible. Thewidth to length ratio is a way to obtain such a uniform concentration ofthe slag bath. As illustrated in FIG. 1, the inlet port 7 is situated inthe corner at the greater distance from the outlet port 8, so that theflow line of the slag across the fuming furnace horizontal plane is aslong as is feasible. It is clear that with a ratio range of 1 :: 6, theflow line will be the longest possible. A greater distance between theseports means a uniform concentration, and therefore a uniform treatment.A ratio of 1 :: 4 is adequate for the purposes of the present invention.

It will be noted also that the disposition of the inlet port 7 at 500 mmover the non-agitated top surface of the slag in the fuming furnace 6also contributes to the uniform concentration of the slag therein. Theslag falls in cascade fashion into the furnace 6, and is thoroughlymixed with the slag in the furnace when agitated. Furthermore, the slagis charged in the fuming furnace 6 in one direction and is discharged ina direction at a right angle to the first direction. This is also anadvantage for the uniform concentration of the slag in the fumingfurnace. The above-described arrangement is critical for the propertreatment of the slag in the fuming furnace 6 in order to recover a highyield of metallic values from the slag in a continuous mode.

The method and apparatus of the present invention make it possible tocontinuously carry out the blasting of the slag in the fuming furnace 6.In this way, all of the drawbacks inherent in the batch methods areavoided and the capacity or size of the aggregate may be increased bymore than 30% with the method and apparatus of the invention. Inaddition, it is possible to provide conditions which render theoperations completely automatic so that the tapping-off and conveying ofthe slag from the shaft furnace all the way to the chute 9 can becontinuously carried out in an automatic manner.

Although the invention is illustrated and described with reference toone preferred embodiment thereof, it is to be expressly understood thatit is in no way limited to the disclosure of such a preferredembodiment, but is capable of numerous modifications within the scope ofthe appended claims.

What is claimed is:
 1. A method for the recovery of non-ferrous metals,comprising the steps of continually introducing an oxygen-containing gasunder superatmospheric pressure into a shaft furnace containing acarbonaceous fuel and a mixture of agglomerates of non-ferrous metalconcentrates to form a layer of molten metal and a superposed layer ofmolten slag at the bottom of the shaft furnace, separately tapping themetal layer and the slag from the bottom of the shaft furnace, flowingthe tapped slag from the shaft furnace directly into a separate settlingtank whereby a mixture of recoverable metal particles and the slagsettles and defines a layer below the slag in the settling tank, locallyheating the slag in the settling tank above the level of the settledmetal particle layer but below the surface of the slag, continuallydischarging the heated slag from the settling tank to a first locationof a separate slag-containing fuming furnace at a level substantiallyabove the level of the slag already present in the fuming furnace,agitating the resulting slag mixture in the fuming furnace, andcontinuously tapping the slag mixture from the fuming furnace.
 2. Amethod as defined in claim 1, wherein the agglomerates are leadconcentrates.
 3. A method as defined in claim 1, in which the step offlowing the slag from the shaft furnace to the settling tank comprisessyphoning the slag into the settling tank.
 4. A method as defined inclaim 1, in which the introducing step comprises gravity-flowing theheated slag to the first location of the fuming furnace.
 5. A method asdefined in claim 1, in which the tapping step comprises withdrawing theslag mixture from the fuming furnace at a point of the slag mixture thatis below and opposite to the first location.